Mouth guard and sheet for mouth guard

ABSTRACT

A mouth guard which is excellent in impact absorbability and durability, is thin and has good fittability, and is able to easily chew thereupon, and does not give vomiting feel; and a sheet for mouth guard which is suitable for producing the mouth guard.  
     The mouth guard or the sheet for mouth guard comprises at least one block copolymer selected from the group consisting of a block copolymer (a-1) comprising polymer blocks A made of a vinyl aromatic compound, and polyisoprene blocks B having a content of 1,2-bonds and 3,4-bonds of 40% by mol or less; a block copolymer (a-2) comprising polymer blocks A, and polymer blocks C which contain an isoprene unit and a butadiene unit in a ratio of from 5/95 to 95/5 (% by weight) and have a content of 1,2-bonds and 3,4-bonds of 40% by mol or less; and a block copolymer (a-3) comprising polymer blocks A, and polybutadiene blocks D having a content of 1,2-bonds of 60% by mol or more, wherein a content of vinyl aromatic compound units in each of the copolymers is from 10 to 40% by weight, and a hydrogenated product thereof (b-1) to (b-3).

TECHNICAL FIELD

[0001] The present invention relates to a mouth guard which is excellentin impact absorbability and durability (tear resistance), and isexcellent in fittability because of being made thinner than conventionalproducts, and able to easily chew thereupon without giving any vomitingfeel, and a sheet for the mouth guard.

BACKGROUND ART

[0002] A mouth guard is employed for the purpose of preventing a brainconcussion and protecting teeth, oral cavity, lips, jaw bones or thelike, and it is rather mandatory particularly in contact athletic sportssuch as American football and boxing. While various materials are usedto produce mouth guards, one used largely in these days is anethylene-vinyl acetate copolymer (hereinafter sometimes abbreviated asEVA). Besides the copolymers, there are mouth guards made of apolyolefinic rubber, silicone rubber, an ethylene-vinyl acetatecopolymer supplemented with a thermoplastic polycaprolactone asdisclosed in Japanese Patent Gazette No. 2594830. However, since aconventional mouth guard produced from an EVA alone has a low impactabsorbability, there has been necessitated to increase its thickness(about 4 mm) in order to increase the impact absorption. Therefore,there are some problems of being not easily conversable, not easilybreathing and the like. In addition, the mouth guard has a poordurability, which experiences a tear due to cracks developed during use.Furthermore, the shape of the mouth guard is deformed over a longperiod, so that the fittability tends to be worsened.

[0003] For the reasons described above, there has been proposed inJapanese Patent Laid-Open No. 2001-54610 a mouth guard compositioncomprising a styrene block copolymer component having excellentdurability, an aliphatic saturated hydrocarbon-based resin and/or anester gum component for giving an impact absorbability and a softeningproperty at a low temperature, and an organopolysiloxane component forreducing stickiness during handling. However, since three or morematerials are used as composite relative to a conventional method usingan EVA material alone, there are some problems in that processabilityduring the production is worsened, and the equipments become toocomplicated. In addition, recently, it has been known that a mouse guardclearly has an effect of improving athletic sport performance inaddition to the purpose of protecting a brain concussion and protectingteeth, oral cavity, lips, jaw bones or the like. The reasons thereforare considered to be an improved occlusion of the palates and an abilityof being able to chew strongly so that a greater power can be exerted.For these purposes, it is important that the mouth guard has anexcellent fittability (fitting feel) and is easily chewed upon withoutcausing any vomiting feel due to a feel of a foreign feel (peculiar odoror taste). However, in the above technique, since an organopolysiloxaneis contained in an amount of 0.1 to 10% by weight in the composition,there are some problems that the mouth guard has insufficientfittability so that the mouth guard is disengaged easily, or that themouth guard gives a vomiting feel.

DISCLOSURE OF INVENTION

[0004] An object of the present invention is to provide a mouth guardwhich is excellent in impact absorbability, durability (tear resistance)and fittability, and able to easily chew thereupon, and does not givevomiting feel; and a sheet for mouth guard which is suitable forproducing the mouth guard.

[0005] As a result of intensive studies in order to solve the aboveproblems, the present inventors have found that a mouth guard being notonly excellent in impact absorbability and durability (tear resistance)but also being excellent in fittability and able to easily chewthereupon without giving any vomiting feel can be obtained by using astyrenic block copolymer having a particular micro-structure as a maincomponent. The present invention has been accomplished thereby.

[0006] Specifically, the present invention relates to a mouth guardcomprising at least one block copolymer selected from the groupconsisting of:

[0007] a block copolymer (a-1) comprising one or more polymer blocks Amade of a vinyl aromatic compound, and one or more polyisoprene blocks Bhaving a content of 1,2-bonds and 3,4-bonds of 40% by mol or more,wherein a content of vinyl aromatic compound units is from 10 to 40% byweight, and a hydrogenated product thereof (b-1);

[0008] a block copolymer (a-2) comprising one or more polymer blocks Amade of a vinyl aromatic compound, and one or more polymer blocks Cwhich contain an isoprene unit and a butadiene unit in a ratio of from5/95 to 95/5 (% by weight) and have a content of 1,2-bonds and 3,4-bondsof 40% by mol or more, wherein a content of vinyl aromatic compoundunits is from 10 to 40% by weight, and a hydrogenated product thereof(b-2); and

[0009] a block copolymer (a-3) comprising one or more polymer blocks Amade of a vinyl aromatic compound, and one or more polybutadiene blocksD having a content of 1,2-bonds of 60% by mol or more, wherein a contentof vinyl aromatic compound units is from 10 to 40% by weight, and ahydrogenated product thereof (b-3).

[0010] Further, the present invention relates to a sheet for mouth guardcomprising at least one block copolymer selected from the groupconsisting of:

[0011] a block copolymer (a-1) comprising one or more polymer blocks Amade of a vinyl aromatic compound, and one or more polyisoprene blocks Bhaving a content of 1,2-bonds and 3,4-bonds of 40% by mol or more,wherein a content of vinyl aromatic compound units is from 10 to 40% byweight, and a hydrogenated product thereof (b-1);

[0012] a block copolymer (a-2) comprising one or more polymer blocks Amade of a vinyl aromatic compound, and one or more polymer blocks Cwhich contain an isoprene unit and a butadiene unit in a ratio of 5/95to 95/5 (% by weight) and have a content of 1,2-bonds and 3,4-bonds of40% by mol or more, wherein a content of vinyl aromatic compound unitsis from 10 to 40% by weight, and a hydrogenated product thereof (b-2);and

[0013] a block copolymer (a-3) comprising one or more polymer blocks Amade of a vinyl aromatic compound, and one or more polybutadiene blocksD having a content of 1,2-bonds of 60% by mol or more, wherein a contentof vinyl aromatic compound units is from 10 to 40% by weight, and ahydrogenated product thereof (b-3).

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] The polymer block A in the block copolymers (a-1), (a-2) and(a-3) employed in the present invention comprises a vinyl aromaticcompound. The vinyl aromatic compound includes, for instance, styrene,α-methylstyrene, 1-vinylnaphthalene, 3-methylstyrene, 4-propylstyrene,4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene,4-(phenylbutyl)styrene and the like. Among them, styrene is preferred.

[0015] The number-average molecular weight of the polymer block A is notparticularly limited. It is preferably within a range of from 2500 to50000, more preferably within a range of from 2500 to 20000. Thenumber-average molecular weight can be determined by a method describedin Examples set forth below.

[0016] It is necessary that the content of the vinyl aromatic compoundunits constituting the polymer block A in the block copolymer is withina range of from 10 to 40% by weight, preferably from 15 to 40% byweight, for any of polymers (a-1), (a-2) and (a-3). When the content ofthe vinyl aromatic compound units in the block copolymer is less than10% by weight, mechanical strength of the block copolymer becomesinsufficient. On the other hand, when the content of the vinyl aromaticcompound units in the block copolymer exceeds 40% by weight, impactabsorbability is impaired.

[0017] In the present invention, the content of 1,2-bonds and 3,4-bonds(content of vinyl bonds) in the polyisoprene block B, the polymer blockC and the polybutadiene block D constituting the block copolymer(provided that the polybutadiene block D contains only the 1,2-bonds;hereinafter referred to the same) is very important in order to exhibitthe impact absorbability required for the mouth guard. In other words, aconventional mouth guard made of an EVA-based resin is less likely toabsorb the impact satisfactorily as evident from the determination by aLuebke rebound resilience test or the like, and impact absorbability isinsufficient in the same manner as in the EVA-based resin when thecontent of 1,2-bonds and 3,4-bonds of the polyisoprene block B, thepolymer block C and the polybutadiene block D constituting the blockcopolymer is low because a rubber-like resilient characteristic isstrong. Since the 1,2-bonds and 3,4-bonds are present at a given levelor more in the polyisoprene block B, the polymer block C and thepolybutadiene block D constituting the block copolymer of the presentinvention as described below, the block copolymer has a satisfactoryimpact absorbability.

[0018] In addition, the mouse guard using a rubber-like highly resilientresin gives a poor fitting when being chewed thereupon. However, sincethe block copolymer as defined in the present invention comprises thepolyisoprene block B, the polymer block C and the polybutadiene block D,each having 1,2-bonds and 3,4-bonds at a given level or more, the mouthguard made of the above block copolymer exhibits a satisfactory fit inthe mouth and is easily chewed thereupon.

[0019] Therefore, it is necessary that the content of 1,2-bonds and3,4-bonds in the polyisoprene block B constituting the block copolymer(a-1) is 40% by mol or more, preferably from 45 to 90% by mol, morepreferably from 50 to 80% by mol. When the content of 1,2-bonds and3,4-bonds is less than 40% by mol, impact absorbability becomesinsufficient and resilient feel becomes too strong when chewedthereupon, so that the fittability (fitting feel) of the mouth guard isimpaired.

[0020] The number-average molecular weight of the polyisoprene block Bis not particularly limited. The number-average molecular weight ispreferably within a range of from 10000 to 300000, more preferablywithin a range of from 100000 to 200000.

[0021] It is necessary that the content of 1,2-bonds and 3,4-bonds inthe polymer block C in the block copolymer (a-2) is 40% by mol or more,preferably 45% by mol or more, more preferably 50% by mol or more. Whenthe content of 1,2-bonds and 3,4-bonds is less than 40% by mol, impactabsorbability is insufficient, and resilient feel becomes too strongwhen chewed thereupon, so that the fittability (fitting feel) of themouth guard is impaired. As to the polymer block C, it is necessary thatisoprene units and butadiene units are contained in a ratio of from 5/95to 95/5 (% by weight), preferably from 10/90 to 90/10 (% by weight). Inthe isoprene units and the butadiene units constituting the polymerblock C, if the content of the isoprene units exceeds 95% by weight, itsglass transition point (Tg) becomes too high, so that the flexibility isimpaired, in a case where the content of 1,2-bonds and 3,4-bonds becomeshigher than 85% by mol.

[0022] The polymerization forms of isoprene units and butadiene unitsconstituting the polymer block C are not particularly limited. Thepolymerization forms may be any of random, block, tapered and otherforms.

[0023] The number-average molecular weight of the polymer block C is notparticularly limited. The number-average molecular weight is preferablywithin a range of from 10000 to 300000, more preferably within a rangeof from 10000 to 200000.

[0024] It is necessary that the content of 1,2-bonds of thepolybutadiene block D in the block copolymer (a-3) is 60% by mol ormore, preferably 80% by mol or more, more preferably 85% by mol or more.When the content of 1,2-bonds is less than 60% by mol, mechanicalproperties, impact strength and durability of the mouth guard areimpaired, and resilient feel becomes too strong when chewed thereupon,so that the fittability of the mouth guard (fitting feel) is impaired.

[0025] The number-average molecular weight of the polymer block D is notparticularly limited. The number-average molecular weight is preferablywithin a range of from 10000 to 300000, more preferably within a rangeof from 10000 to 200000.

[0026] The content of vinyl bonds of the present specification can bedetermined by the method described in Examples set forth below.

[0027] The binding form of each polymer block in the block copolymer isnot particularly limited. The binding form may be linear or branchedbinding, or any combination thereof. Concrete examples of the molecularstructure of the block copolymer include A(BA)n, (AB)n, A(CA)n, (AC)n,A(DA)n, (AD)n, and the like, wherein A is a polymer block A made of avinyl aromatic compound, B is a polyisoprene block B, C is a polymerblock C made of isoprene units and butadiene units, D is a polybutadieneblock D, and n is an integer of 1 or more. In addition, as the blockcopolymer, there can be used those having a stellate (for example,[(AB)mX], wherein m is an integer of 2 or more, X is a residue of acoupling agent) molecular structure, obtained by using divinyl benzene,a tin compound, a silane compound or the like as a coupling agent.

[0028] The individual block copolymers may comprise only a single kindof molecular structure. Alternatively, the individual block copolymermay be a combination of two or more different kinds of molecularstructures, such as a mixture of a triblock type and a diblock type.

[0029] The number-average molecular weight of the above block copolymeris preferably within a range of from 12000 to 400000, more preferablywithin a range of from 30000 to 300000.

[0030] In the present invention, there can be also used hydrogenated(hereinafter simply referred to as “hydrogenated”) products of the blockcopolymers (a-1), (a-2) and (a-3) [block copolymers (b-1), (b-2) and(b-3)].

[0031] As processes for preparing the block copolymers (a-1), (a-2) and(a-3), any known processes can be utilized. The processes include, forinstance, the following processes (i) to (iii):

[0032] (i) a process comprising polymerizing a vinyl aromatic compoundusing an alkyllithium compound as a polymerization initiator, andthereafter sequentially polymerizing a conjugated diene compound(isoprene and/or butadiene) and a vinyl aromatic compound thereto;

[0033] (ii) a process comprising polymerizing a vinyl aromatic compoundand thereafter a conjugated diene compound (isoprene and/or butadiene),and coupling the resulting block copolymer using a coupling agent; and

[0034] (iii) a process comprising polymerizing a conjugated dienecompound (isoprene and/or butadiene) using a dilithium compound as apolymerization initiator, and thereafter sequentially polymerizing avinyl aromatic compound thereto.

[0035] In the process described above, as the alkyllithium compound,there may be used, for instance, a compound of which alkyl group has 1to 10 carbon atoms. Among them, methyllitium, ethyllithium,pentyllithium, n-butyllithium, s-butyllithium and t-butyllithium arepreferred. In addition, the coupling agent includes, for instance,halogenated compounds such as dichloromethane, dibromomethane,dichloroethane, dibromoethane, dibromobenzene and tin tetrachloride;ester compounds such as phenyl benzoate and ethyl acetate;divinylbenzene; various silane compounds; and the like. Further, thedilithium compound includes, for instance, naphthalenedilithium,dilithiohexylbenzene and the like.

[0036] The amount of the polymerization initiator or coupling agentmentioned above used may be appropriately determined depending upon thedesired molecular weight of the block copolymer. Usually, thepolymerization initiator is used within a range of from 0.01 to 0.2parts by weight, and the coupling agent is used within a range of from0.04 to 0.8 parts by weight, based on 100 parts by weight of the entiremonomers used in the polymerization.

[0037] In addition, the content of 1,2-bonds and 3,4-bonds in thepolyisoprene block B, the polymer block C and the polybutadiene block D(hereinafter simply referred to as conjugated diene block in some cases)can be controlled by using a Lewis base as a cocatalyst uponpolymerization. The above Lewis base includes, for instance, ethers suchas dimethyl ether, diethyl ether and tetrahydrofuran; glycol ethers suchas ethylene glycol dimethyl ether and diethylene glycol dimethyl ether;amine-based compounds such as triethylamine, N,N,N′,N′-tetramethylethylenediamine (hereinafter simply referred to as TMEDA) andN-methylmorpholin; and the like. The amount of the Lewis base used is,for instance, within a range of from 0.1 to 1000 mols per mol of thelithium atom in the polymerization initiator.

[0038] In the polymerization, an organic solvent which is inert to thepolymerization initiator is used as a solvent. As the solvent, it ispreferable to use an aliphatic hydrocarbon having 6 to 12 carbon atomssuch as hexane and heptane, an alicyclic hydrocarbon such as cyclohexaneand methylcyclohexane, and an aromatic hydrocarbon such as benzene.

[0039] The polymerization is carried out usually within a temperaturerange of from 0° to 80° C. in any of the above polymerization processes(i) to (iii). The reaction time is usually from 0.5 to 50 hours.

[0040] The block copolymers (a-1), (a-2) and (a-3) obtained by theprocesses described above may be hydrogenated as desired. For example,each of hydrogenated block copolymers (b-1), (b-2) and (b-3) can beproduced by employing a known process, for instance, a process in whicha molecular hydrogen is reacted with the block copolymers using a knownhydrogenation catalyst in a solution state of the block copolymersdissolved in a solvent inert to the reaction. As the hydrogenationcatalyst used herein, there may, for instance, be used a heterogeneouscatalyst made of a Raney nickel, a metal such as Pt, Pd, Ru, Rh or Nisupported to a carrier made of carbon, alumina, diatomaceous earth, orthe like; a Ziegler catalyst comprising a combination of anorganometallic compound comprising a metal of Group VIII such as nickelor cobalt with an organoaluminum compound such as triethylaluminium ortriisobutyl aluminum, an organolithium compound or the like; ametallocene catalyst comprising a combination of a bis(cyclopentadienyl)compound of a transition metal such as titanium, zirconium or hafniumwith an organometallic compound such as lithium, sodium, potassium,aluminum, zinc or magnesium; and the like. The hydrogenation is carriedout usually under a hydrogen pressure within a range of from anatmospheric pressure to 200 MPa and a reaction temperature within arange of from room temperature to 250° C. The reaction time is usuallyfrom 0.1 to 100 hours. The degree of the hydrogenation is preferablyfrom about 20 to about 100% as a hydrogenation ratio.

[0041] The block copolymer thus obtained can be collected by (i)solidifying a reaction liquid mixture, for instance, with methanol,followed by heating or drying under a reduced pressure, or (ii) pouringa reaction solution into a boiling water to remove the solventazeotropically in a so-called steam-stripping, followed by heating ordrying under a reduced pressure.

[0042] The mouth guard can be prepared by using a raw material resincomprising one block copolymer selected from the group consisting of theblock copolymers (a-1), (a-2) and (a-3) obtained as above and thehydrogenated products thereof (b-1), (b-2) and (b-3), or comprising acombination of those in a given ratio, or using a sheet for mouth guardprepared by subjecting the above resin to a given molding process suchas extrusion molding, calendar molding, press molding or injectionmolding. As the thickness of the sheet, the thinner the more preferable,from the viewpoint of prevention from any hindrances during acompetition game, conversation or breathing when the mouth guard iscontained in the oral cavity. However, since a certain level of thethickness is necessary from the viewpoint of the properties needed forthe protection of the oral cavity, the thickness of the sheet ispreferably from 0.5 to 5 mm, more preferably from 1 to 4 mm. Among theresins mentioned above, it is especially preferable to use the blockcopolymer (a-1) and/or (b-1), because the mouth guard obtained is easilychewed thereupon and has excellent impact absorbability.

[0043] The raw material resin described above can contain variousadditives, such as antioxidants, ultraviolet absorbents, lightstabilizers, colorants, crystal-nucleating agent, antibacterial agentsand antifungal agents, as desired, within the range so that the effectsof the present invention are not impaired. The amount of these additivesused is usually within a range of from 0.01 to 5 parts by weight basedon 100 parts by weight of the resin. In addition, there can beformulated a rein having little agglutination property, including apolyolefin resin such as a polyethylene, a polypropylene, anethylene-propylene copolymer, an ethylene-α-olefin copolymer, ahydrogenated polyisoprene, a hydrogenated polybutadiene, a butyl rubber,a polyisobutylene, a polybutene, an ethylene-vinyl acetate copolymer, anethylene-methacrylic acid copolymer, an ethylene-acrylic acid copolymer,or an ethylene-ethyl acrylate copolymer as desired, within the range sothat the effects of the present invention are not impaired.

[0044] The present invention also encompasses the sheet for mouth guardmentioned above.

[0045] For instance, the mouth guard of the present invention can beprepared by roughly two different methods. In both methods, animpression of the jaw of user is previously obtained. For instance, animpression of the jaw of the user is obtained with an alginateimpression material on an commercially available tray. Thereafter, aplaster is poured onto the tray in which the impression is obtained, andthe plaster is hardened, thereby preparing a plaster jaw model. One ofthe methods for preparing a mouth guard is a method comprisingpreviously preparing a sheet for mouth guard, heating this sheet with,for example, a heater until the sheet is softened, contouring the sheetwith the jaw model of the user by vacuum molding or the like, therebypreparing a mouth guard matching the oral cavity of the user. Besidesthe vacuum molding, there can be employed pressure molding, vacuumpressure molding, heat press molding or the like. The other methodcomprises preparing a concave mold capable of pouring the resinthereinto on the basis of the jaw model, pouring the raw material resindescribed above thereinto, thereby preparing a mouth guard.

[0046] The mouth guard or the sheet for mouth guard of the presentinvention can be used in the form of a laminate, which is produced bylaminating on a surface of the mouth guard or the sheet for mouth guard,layers made of a resin having little agglutination property, such as apolyolefin resin including a polyethylene, a polypropylene, anethylene-propylene copolymer, an ethylene-α-olefin copolymer, ahydrogenated polyisoprene, a hydrogenated polybutadiene, a butyl rubber,a polyisobutylene, a polybutene, an ethylene-vinyl acetate copolymer, anethylene-methacrylic acid copolymer, an ethylene-acrylic acid copolymer,or an ethylene-ethyl acrylate copolymer as desired, within the range sothat the effects of the present invention are not impaired.

[0047] As the mouth guard or the sheet for mouth guard of the presentinvention, those containing 85% by weight or more of a block copolymerselected from the group consisting of the block copolymers (a-1), (a-2)and (a-3) of the present invention and hydrogenated products thereof(b-1), (b-2) and (b-3) are preferable, especially 90% by weight or more.

[0048] The mouth guard obtained as described above has excellent impactabsorbability, durability (tear resistance) and fittability, is easilychewed thereupon, and gives no vomiting feel. Furthermore, since themouth guard of the present invention has excellent impact absorbability,the mouth guard can be made thinner than that of a conventional product,thereby greatly contributing to the improvement in the fittability.

EXAMPLES

[0049] The present invention will be described by referring to thefollowing Examples without intending to limit the present inventionthereto. As the test methods in Examples, the following methods areemployed.

[0050] (Content of Styrene)

[0051] The content was calculated from the weight of each monomercomponent used in the polymerization.

[0052] (Number-Average Molecular Weight)

[0053] The number-average molecular weight (Mn) calculated aspolystyrene was obtained by a GPC determination.

[0054] (Content of Vinyl Bonds)

[0055] A block copolymer not subjected to hydrogenation was dissolved ina deuterated chloroform (CDCl₃), and ¹H-NMR spectrum was determined, andthe content of vinyl bonds (content of 1,2-bonds and 3,4-bonds) wascalculated from the peak area ascribed to isoprene and/or butadiene andthe peak area corresponding to 1,2-bonds and 3,4-bonds.

[0056] (Hydrogenation Ratio)

[0057] Iodine values of a block copolymer before and after thehydrogenation were determined, and the hydrogenation ratio wascalculated from the values obtained.

[0058] (Tensile Test)

[0059] The tensile strength at break, the tensile elongation at breakand the tensile modulus were determined using a dumbbell-shaped No. 3test piece as prescribed in JIS K6251 with a mechanical strengthdetermining device at a test speed of 200 mm/min, a distance betweenchucks of 70 mm, a distance between reference marks of 25 mm and a testpiece temperature of 23° C.

[0060] (Tensile Impact Strength)

[0061] The tensile impact strength was determined using a dumbbell-typeL test piece as prescribed in ASTM D1822 at a weight of a hammer of3.970 kg, a distance between a shaft of the hammer and a center ofgravity of 22.06 cm, a lift angle of the hammer of 135°, and a testpiece temperature of 37° C.

[0062] (Tear Test)

[0063] The tear strength and the elongation at break (tear elongation)were determined using a notched angled test piece as prescribed in JISK6252 at a test speed of 500 mm/min and a test piece temperature of 37°C.

[0064] (Durometer Hardness Test)

[0065] As prescribed in JIS K6253, the hardness was determined bystacking three 2-mm thick sheets. The determination was made with a typeA durometer at a test piece temperature of 25.5° C.

[0066] (Chewability)

[0067] From questionnaire results after asking fifty senior high schoolrugby football players as monitors to wear mouth guards during practiceand games for 3 months, the fittability was numerically expressed (0 to100 points) by multiplying the following evaluation score by the numberof the players.

[0068] 2: very chewable,

[0069] 1: moderate, and

[0070] 0: very repelling and not easily chewable.

[0071] (Vomiting Feel)

[0072] From questionnaire results after asking fifty senior high schoolrugby football players as monitors to wear mouth guards during practiceand games for 3 months, the vomiting feel was numerically expressed (0to 100 points) by multiplying the following evaluation score by thenumber of the players.

[0073] 2: completely no vomiting feel,

[0074] 1: slight vomiting feel, and

[0075] 0: severe vomiting feel.

Example 1

[0076] Styrene was polymerized at 60° C. in a dried, nitrogen-replacedpressure vessel using cyclohexane as a solvent and s-butyllithium as apolymerization initiator, and thereafter TMEDA was added thereto as aLewis base. Next, isoprene and styrene were sequentially polymerized,thereby obtaining a styrene-isoprene-styrene block copolymer. Theresulting block copolymer had a content of styrene of 20% by weight, anumber-average molecular weight of 103000 and a content of vinyl bonds(content of 1,2-bonds and 3,4-bonds) of 75% by mol. Table 1 summarizesthe properties of the block copolymers obtained in Example 1, andExamples 2 to 5 and Comparative Examples 3 and 4 described below.

[0077] The resulting block copolymer was subjected to pressure moldingat 150° C. to give a sheet for mouth guard having a thickness of 2 mm.The tensile test, the tensile impact test, the tear test and thedurometer hardness test were carried out using this sheet. The resultsare shown in Table 2.

[0078] This sheet was also subjected to a Luebke rebound resilience testas prescribed in JIS 6255. As a result, there was confirmed that theimpact was absorbed very rapidly upon impact as shown by 7% (firsttime), 0.6% (second time) and 0.2% (third time).

[0079] The determinations of each of the properties were made using asheet for mouth guard. However, the properties of the sheet show theproperties of mouth guard put on directly because the mouth guard wasobtained by molding the sheet.

[0080] Subsequently, an impression was collected from a user (monitor)to produce a plaster model, and the sheet prepared was attached to asuction-type vacuum molding machine. The sheet was softened at a settemperature of 150° C., and thereafter a vacuum pump was operated withsuction to mold the sheet. The molded sheet was trimmed to prepare amouth guard. During the preparation of the mouth guard, the sheet hadexcellent operability without giving a sticky feel to the plaster modelor fingers. There were obtained evaluations from the users that themouth guard thus obtained had excellent durability and impactabsorbability. The chewability and the vomiting feel were also evaluatedby the above methods. The results are shown in Table 2.

Examples 2 to 4

[0081] The evaluations were made in the same manner as in Example 1using a styrene-isoprene-styrene block copolymer (Example 2), astyrene-isoprene/butadiene-styrene block copolymer (Example 3) or astyrene-butadiene-styrene block copolymer (Example 4) shown in Table 1,which was prepared in the same manner as that in Example 1. The resultsare shown in Table 2.

Example 5

[0082] The evaluations were made in the same manner as in Example 2except that a resin prepared by hydrogenating thestyrene-isoprene-styrene block copolymer obtained in Example 2 was used.The results are shown in Table 2.

Comparative Example 1

[0083] A sheet for mouth guard made of an ethylene-vinyl acetatecopolymer (manufactured by Company “S”) was subjected to pressuremolding at 150° C. to give a sheet having a thickness of 2 mm. The testswere carried out in the same manner as in Example 1 using this sheet.The results are shown in Table 2. This sheet was subjected to a Luebkeimpact resiliency test as prescribed in JIS 6255. As a result, it wasfound that the impact was absorbed very slowly upon impact as shown by62% (first time), 41% (second time), 27% (third time), 18% (fourthtime), 12% (fifth time) and 8.5% (sixth time).

Comparative Example 2

[0084] A resin composition comprising a composition of: copolymer(content of 1,2-bonds: 15% by mol) of 67% by wt. polystyrene (30% bywt.) and polybutadiene (70% by wt.) ester gum (glycerin ester of rosin)25% by wt. methylstyryl-modified dimethylpolysiloxane  8% by wt.

[0085] was molded to give a sheet having a thickness of 2 mm. The testswere carried out in the same manner as in Example 1 using this sheet.The results are shown in Table 2.

Comparative Examples 3 and 4

[0086] Evaluations were made in the same manner as in Example 1 using astyrene-isoprene-styrene block copolymer shown in Table 1 prepared inthe same manner as that in Example 1. The results are shown in Table 2.TABLE 1 Number- Isoprene/ Average Styrene Butadiene Content of MolecularHydro- Content Content Vinyl Bonds Weight genation (% by wt.) (% by wt.)(% by mol.) (Mn) Ratio (%) Ex. 1 20 80/0  75 103000 0 Ex. 2 20 80/0  55120000 0 Ex. 3 20 40/40 80 127000 0 Ex. 4 35  0/65 75 180000 0 Ex. 5 2080/0  56 124000 95 (Before Hydro- genation Comp. 50 50/0  75 110000 0Ex. 3 Comp. 20 80/0  25 115000 97 Ex. 4 (Before Hydro- genation

[0087] TABLE 2 Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex.1 Ex. 2 Ex. 3 Ex. 4 Tensile 7 4 4 3 5 9 3 13 8 Modulus (MPa) Tensile 650620 580 650 600 430 670 720 410 Impact Strength (kJ/m²) Tensile 10 11 1011 10 10 9 8 14 Strength at Break (MPa) (Break Pt.) Tensile 900 1000 8501000 800 1200 900 700 1250 Elongation at Break (%) (Break Pt.) Tear 2.02.1 2.0 2.4 2.0 2.0 2.2 2.5 1.9 Strength (MPa) (Break Pt. at 37° C.)Tear 260 280 300 220 290 90 180 160 270 Elongation (%) (Break Pt. at 37°C.) Durometer 61 57 59 80 64 77 63 98 67 Hardness (JIS-A) Chewability 8892 75 80 80 22 40 16 50 (Score) Lack of 92 90 90 85 85 55 35 92 90Vomiting Feel (Score)

[0088] As is clear from Examples 1 to 5 of Table 2, the mouth guard ofthe present invention gave excellent results in all of the evaluationitems as compared to those of Comparative Examples 1 to 4. It can beseen from the above that the mouth guard of the present invention hasexcellent impact absorbability, tear elongation at break and chewabilityand does not give any vomiting feel. The excellent tear elongation atbreak means that a breakage of the sheet due to cracks made upon use isless likely to be generated, and thereby showing excellent durability.

Industrial Applicability

[0089] According to the present invention, there are provided a mouthguard, which sufficiently alleviates an external pressure and issuitable for protecting dentine and jaw bones, and also is excellent indurability and easily chewed with hardly giving a vomiting feel, and asheet for mouth guard suitable for the production of the mouth guard.

1. A mouth guard comprising at least one block copolymer selected fromthe group consisting of: a block copolymer (a-1) comprising one or morepolymer blocks A made of a vinyl aromatic compound, and one or morepolyisoprene blocks B having a content of 1,2-bonds and 3,4-bonds of 40%by mol or more, wherein a content of vinyl aromatic compound units isfrom 10 to 40% by weight, and a hydrogenated product thereof (b-1); ablock copolymer (a-2) comprising one or more polymer blocks A made of avinyl aromatic compound, and one or more polymer blocks C which containan isoprene unit and a butadiene unit in a ratio of from 5/95 to 95/5 (%by weight) and have a content of 1,2-bonds and 3,4-bonds of 40% by molor more, wherein a content of vinyl aromatic compound units is from 10to 40% by weight, and a hydrogenated product thereof (b-2); and a blockcopolymer (a-3) comprising one or more polymer blocks A made of a vinylaromatic compound, and one or more polybutadiene blocks D having acontent of 1,2-bonds of 60% by mol or more, wherein a content of vinylaromatic compound units is from 10 to 40% by weight, and a hydrogenatedproduct thereof (b-3).
 2. A sheet for mouth guard comprising at leastone block copolymer selected from the group consisting of: a blockcopolymer (a-1) comprising one or more polymer blocks A made of a vinylaromatic compound, and one or more polyisoprene blocks B having acontent of 1,2-bonds and 3,4-bonds of 40% by mol or more, wherein acontent of vinyl aromatic compound units is from 10 to 40% by weight,and a hydrogenated product thereof (b-1); a block copolymer (a-2)comprising one or more polymer blocks A made of a vinyl aromaticcompound, and one or more polymer blocks C which contain an isopreneunit and a butadiene unit in a ratio of from 5/95 to 95/5 (% by weight)and have a content of 1,2-bonds and 3,4-bonds of 40% by mol or more,wherein a content of vinyl aromatic compound units is from 10 to 40% byweight, and a hydrogenated product thereof (b-2); and a block copolymer(a-3) comprising one or more polymer blocks A made of a vinyl aromaticcompound, and one or more polybutadiene blocks D having a content of1,2-bonds of 60% by mol or more, wherein a content of vinyl aromaticcompound units is from 10 to 40% by weight, and a hydrogenated productthereof (b-3).